Disordered surfaces: a smoothed He-target scattering potential for metal atoms adsorbed on metal surfaces

Abstract

The theoretical interpretation of experimental results on He scattering from metal adatoms epitaxially grown on metal substrates makes use, in general, of an interaction potential that, as far as the He-adatom interaction is concerned, is a pairwise sum of Lennard-Jones ( V LJ) terms. This approach results in more corrugated metal surfaces than expected on the basis of both experimental data and qualitative considerations on the contribution of the electron densities of the metal adatoms to the repulsive part of the interaction potential. The present work suggests a very simple way to significantly reduce or eliminate the surface corrugation by averaging the He-adsorbate potential over a unit cell of the substrate lattice. The so obtained potential ( V AV) was compared with V LJ for the HeAg/Pt(111) colliding system on the basis of turning point surfaces, specular and diffractive intensities vs. surface coverage and angular intensity distribution of scattered atoms, calculated under the sudden approximation. These data show that V AV, although too simple to correctly reproduce all the features of the He-adatom interaction, could represent a useful tool in the study of the growth of metal adlayers.